[RFC PATCH 3/4] drm/etnaviv: Change order of enabling clocks to fix boot on i.MX8MM

[Peng Fan]

> Subject: Re: [RFC PATCH 3/4] drm/etnaviv: Change order of enabling clocks to
> fix boot on i.MX8MM
> 
> On 30.04.20 16:35, Lucas Stach wrote:
> > Am Donnerstag, den 30.04.2020, 12:46 +0000 schrieb Schrempf Frieder:
> >> From: Frieder Schrempf <frieder.schrempf at kontron.de>
> >>
> >> On some i.MX8MM devices the boot hangs when enabling the GPU clocks.
> >> Changing the order of clock initalization to
> >>
> >> core -> shader -> bus -> reg
> >>
> >> fixes the issue. This is the same order used in the imx platform code
> >> of the downstream GPU driver in the NXP kernel [1]. For the sake of
> >> consistency we also adjust the order of disabling the clocks to the
> >> reverse.
> >>
> >> [1]
> >> https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fsou
> >>
> rce.codeaurora.org%2Fexternal%2Fimx%2Flinux-imx%2Ftree%2Fdrivers%2F
> mx
> >>
> c%2Fgpu-viv%2Fhal%2Fos%2Flinux%2Fkernel%2Fplatform%2Ffreescale%2Fgc
> _h
> >>
> al_kernel_platform_imx.c%3Fh%3Dimx_5.4.3_2.0.0%23n1538&data=02
> %7C
> >>
> 01%7Cpeng.fan%40nxp.com%7Cdc7da53f665e4f567e3008d7ed1c27e0%7C6
> 86ea1d3
> >>
> bc2b4c6fa92cd99c5c301635%7C0%7C0%7C637238577497969787&sda
> ta=QRHzu
> >> C6gSKy%2F6y2FTRvlNF5t7DmJIvTgBESYKchI%2FDw%3D&reserved=0
> >
> > I don't see why the order of the clocks is important. Is this really a
> > GPU issue? As in: does a GPU access hang when enabling the clocks in
> > the wrong order? Or is this a clock driver issue with a clock access
> > hanging due to an upstream clock still being disabled?
> 
> Actually you might be right with this being a clock driver issue. The hanging
> happens while enabling the clocks (unrelated to any GPU register access). The
> strange thing is that most of the devices we have don't care and work as is
> and some devices reliably fail each time when enabling the clocks in the
> "wrong" order.
> 
> So I guess this could indeed be some clock being enabled with an upstream
> PLL not having locked yet or something.

https://patchwork.kernel.org/cover/11433775/

Will this pachset help?

The i.MX8M CCM root mux code in Linux needs a fix.

Regards,
Peng.

> 
> >
> > Regards,
> > Lucas
> >
> >> Signed-off-by: Frieder Schrempf <frieder.schrempf at kontron.de>
> >> ---
> >>   drivers/gpu/drm/etnaviv/etnaviv_gpu.c | 42
> +++++++++++++--------------
> >>   1 file changed, 21 insertions(+), 21 deletions(-)
> >>
> >> diff --git a/drivers/gpu/drm/etnaviv/etnaviv_gpu.c
> >> b/drivers/gpu/drm/etnaviv/etnaviv_gpu.c
> >> index 7b138d4dd068..424b2e5951f0 100644
> >> --- a/drivers/gpu/drm/etnaviv/etnaviv_gpu.c
> >> +++ b/drivers/gpu/drm/etnaviv/etnaviv_gpu.c
> >> @@ -1487,55 +1487,55 @@ static int etnaviv_gpu_clk_enable(struct
> etnaviv_gpu *gpu)
> >>   {
> >>   	int ret;
> >>
> >> -	if (gpu->clk_reg) {
> >> -		ret = clk_prepare_enable(gpu->clk_reg);
> >> +	if (gpu->clk_core) {
> >> +		ret = clk_prepare_enable(gpu->clk_core);
> >>   		if (ret)
> >>   			return ret;
> >>   	}
> >>
> >> -	if (gpu->clk_bus) {
> >> -		ret = clk_prepare_enable(gpu->clk_bus);
> >> +	if (gpu->clk_shader) {
> >> +		ret = clk_prepare_enable(gpu->clk_shader);
> >>   		if (ret)
> >> -			goto disable_clk_reg;
> >> +			goto disable_clk_core;
> >>   	}
> >>
> >> -	if (gpu->clk_core) {
> >> -		ret = clk_prepare_enable(gpu->clk_core);
> >> +	if (gpu->clk_bus) {
> >> +		ret = clk_prepare_enable(gpu->clk_bus);
> >>   		if (ret)
> >> -			goto disable_clk_bus;
> >> +			goto disable_clk_shader;
> >>   	}
> >>
> >> -	if (gpu->clk_shader) {
> >> -		ret = clk_prepare_enable(gpu->clk_shader);
> >> +	if (gpu->clk_reg) {
> >> +		ret = clk_prepare_enable(gpu->clk_reg);
> >>   		if (ret)
> >> -			goto disable_clk_core;
> >> +			goto disable_clk_bus;
> >>   	}
> >>
> >>   	return 0;
> >>
> >> -disable_clk_core:
> >> -	if (gpu->clk_core)
> >> -		clk_disable_unprepare(gpu->clk_core);
> >>   disable_clk_bus:
> >>   	if (gpu->clk_bus)
> >>   		clk_disable_unprepare(gpu->clk_bus);
> >> -disable_clk_reg:
> >> -	if (gpu->clk_reg)
> >> -		clk_disable_unprepare(gpu->clk_reg);
> >> +disable_clk_shader:
> >> +	if (gpu->clk_shader)
> >> +		clk_disable_unprepare(gpu->clk_shader);
> >> +disable_clk_core:
> >> +	if (gpu->clk_core)
> >> +		clk_disable_unprepare(gpu->clk_core);
> >>
> >>   	return ret;
> >>   }
> >>
> >>   static int etnaviv_gpu_clk_disable(struct etnaviv_gpu *gpu)
> >>   {
> >> +	if (gpu->clk_reg)
> >> +		clk_disable_unprepare(gpu->clk_reg);
> >> +	if (gpu->clk_bus)
> >> +		clk_disable_unprepare(gpu->clk_bus);
> >>   	if (gpu->clk_shader)
> >>   		clk_disable_unprepare(gpu->clk_shader);
> >>   	if (gpu->clk_core)
> >>   		clk_disable_unprepare(gpu->clk_core);
> >> -	if (gpu->clk_bus)
> >> -		clk_disable_unprepare(gpu->clk_bus);
> >> -	if (gpu->clk_reg)
> >> -		clk_disable_unprepare(gpu->clk_reg);
> >>
> >>   	return 0;
> >>   }
> >